94 SUMMARY OF CURRENT RESEARCHES RELATING TO 



form, with greatly thickened walls. Crystal-cells (containing calcium 

 oxalate) are frequently found, and are distinguished by peculiar 

 properties. In many plants these crystal-cells are divided by trans- 

 verse and longitudinal walls into smaller chambers (Pterocarya, 

 Quercus). As the internodes lengthen they manifest a tendency to 

 become larger than any of the other cells (Sibes, Ledum). They lose 

 their protoplasmic contents at an earlier period, and die before the 

 other cells of the medullary tissue (Euonymus). In many plants, 

 even those in which the pith is lignified, the walls of these crystal- 

 cells consist of cellulose, remaining permanently thin and unligni- 

 fied ; on which account they often collapse and form cavities in the 

 tissue. The pith of some woody plants consists, during its whole exist- 

 ence, of thin soft cellulose. It is then subject to a variety of subse- 

 quent changes, from further division or superficial growth, or the 

 collapse of the tissue after vital activity has ceased. 



Development of Palm-leaves.* — Prof. A. W. Eichler has in- 

 vestigated, in a large number of species, the origin of the division, 

 whether pinnate or digitate, in palm-leaves, which differs from that 

 in other leaves in being not the result of the growth of segments 

 originally distinct, but of splitting or tearing. He finds the order of 

 development to be this : — First, the rachis with the leaf-sheath ; then 

 the lamina in the form of an expansion of the margin of the rachis.' 

 Where there is a petiole, it is of intercalary origin as the leaf 

 unfolds. The lamina grows very rapidly in breadth, and thus pro- 

 duces folds lying very close to one another, arranged in a pinnate or 

 digitate manner according to the length of the rachis; and the 

 lamina then becomes split by the decay of certain angles of these 

 folds. Of this there are four cases, according as it is the upper 

 or lower angles, or both, that decay, or the lateral angles also. In 

 Garludovica, belonging to the PandanaceEe, the processes are similar. 



Contrivances for Storage of Water in the Leaf.t — Dr. E. Hein- 

 richer describes a structure which he has observed especially in the 

 leaves of species of Centaurea growing in very dry situations. The 

 delicate cells of the parenchyma-sheaths which inclose the finer veins 

 of the leaves, and which ordinarily serve for the transfer of a portion 

 of the products of assimilation, are not unfrequently transformed 

 into tracheid-like cells, which then perform a different function, and 

 which the author terms " reserve-traeheids." A similar structure is 

 well developed in Astrolobium repandum, and is described by the 

 author in detail. This is one of a number of contrivances in the 

 mesophyll of the leaf for the rapid transference, or for the storing 

 up of water, corresponding to the needs of the plant as dependent on 

 climate and habitat. In addition to their usual position running 

 alongside the vascular bundles, these reserve tracheids are also 

 sometimes found dispersed through the parenchyma of the leaf. The 



* Abhandl. K. Preuss. Akad. Wiss. Berlin, 1885 (5 pis.). See Naturforscher, 

 xviii. (1885) p. 376. 



t Bot. Oentralbl., xxiii. (1885) pp. 25-31, 56-61 (1 pi.). 



